Temperature compensated planar narrow-band notch filter with fully automated laser-trimming

Abstract

A new narrow-band notch filter using a planar dual mode ring resonator (FCR) is presented. The resonator operates at harmonic frequencies and is manufactured on a temperature stable calcium magnesium titanate substrate, using photo-Lithographic thinfilm processes. An innovative fully automated active laser-trimming procedure is used to adjust the center frequency and the bandwidth of the filter.High unloaded quality factors of more than 400 have been obtained at Ka-baud frequencies. With these high quality factors a 3dBbandwidth of less than 1% in conjunction with a notch depth of more than 40dB can be achieved. In addition, the frequency tuning range of the laser-trimming is larger than 10% without any significant change of the filter characteristic or the quality factor of the resonator. The measured temperature coefficient of the filter is -2ppmJK.We use a notch filter with an electrical length of four wavelengths to suppress the undesired residual local oscillator signal in the transmitter chain of our latest microwave Point-to-point (PP) and Point-to-Multipoint (PMP) transceivers.

Temperature Effect on a Lumped Element Balanced Dual-Band Band-Stop Filter

“…From the fourth column, the filter response is tested for a much higher temperature variation range (80 • C) than [16][17][18] (35 • C-40 • C). For this wide temperature range, the proposed filter shows only 0.2-0.3% shift in center frequency whereas other designs (except [20]) demonstrate at least 0.6% variation for a temperature sweep of only 35 • C (fifth column). Although [20] exhibits only 0.02% shift in center frequency, it shows the maximum fluctuation in the stopband rejection level (15 dB) among all the designs (sixth column).…”

“…For this wide temperature range, the proposed filter shows only 0.2-0.3% shift in center frequency whereas other designs (except [20]) demonstrate at least 0.6% variation for a temperature sweep of only 35 • C (fifth column). Although [20] exhibits only 0.02% shift in center frequency, it shows the maximum fluctuation in the stopband rejection level (15 dB) among all the designs (sixth column). Compared to this, the engineered design is very stable which shows a maximum shift of only 2 dB for a 0.2% shift in resonant frequency.…”

“…The simulation results demonstrate that the resonant frequency shifts about 0.6% for only 49 • C variation in operating temperature. Similarly, in [16][17][18][19][20], the impact of temperature is examined on various band-stop filter architectures. Among them, the designs in [16][17][18] have been tested for a temperature variation range of less than 40 • C, and in this range, they exhibited at least 0.9% shift in their corresponding resonant frequencies.…”

“…Moreover, the stopband rejection in [16] is not satisfactory (maximum 10 dB). Likewise, the temperature change in [19] and [20] affects the filter designs significantly in terms of stopband resonant frequency and stopband rejection, respectively. In comparison to these single-ended designs, differential filters are highly stable in terms of system noise, generation of transient noise, voltage swing, second-order nonlinearities, and speed.…”